DESCRIPTION (taken from the application) Transcriptional activity is dependent not only on the binding of transcription factors to cis-acting elements, but also on the ability of those factors to recruit a complex hierarchy of proteins to stabilize the basal transcriptional machinery. Basal lactotroph specific expression of the rat prolactin (rPRL) promoter is dependent on the interaction of the proto-oncoprotein c-Ets-1, a member of the -Ets family of transcription factors, with the pituitary-specific transcription factor, Pit-1, at a composite Ets/Pit-1 DNA binding element in the rPRL promoter. While each of these factors alone is capable of activating rPRL gene transcription, the combination of these two transcription factors results in a marked synergistic response. Although the precise mechanism for this synergy remains unknown, it is clear that physical interaction of these two factors is required. Recent studies suggest that the activity of Pit-1 and Ets-1 may be determined by the formation of co-regulatory complexes. Thus, I hypothesize that the Pit-1/Ets-1 complex mediates the synergistic response of the rPRL promoter by recruiting specific transcription regulatory proteins. The goals of this study are to map the specific amino acids of Pit-1 and Ets-1 responsible for their physical and functional interaction, and to use liquid chromatography/mass spectrometry methods to identify the protein components that are recruited to the Ets-1/Pit-1 complex. Therefore, these studies are likely to provide critical insights into the molecular mechanisms underlying combinatorial factor interactions and how they mediate synergistic responses. Finally, these studies are important to my career development, as they will allow me to gain expertise in the cutting edge field of proteomics and protein structure-function relationships, which I can then utilize to establish my career as an independent investigator.